Replacement or supplementation of a nucleus pulposus using a hydrogel
a technology of nucleus pulposus and hydrogel, which is applied in the direction of impression caps, prostheses, joint implants, etc., can solve the problems of disc degradation and function loss, and achieve the effect of constant volume of hydrated hydrogel and improved control of implantation intra-operatively
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example 1
[0067] This example illustrates the preparation of a preferred hydrogel used in the practice of the invention.
[0068] An amount of 12.7 g of PVA (Mowiol, supplied by Kuraray Co. Ltd., 132,000 Mw 50,000 Mn PD 2.6; >99.1% hydrolyzed) is mixed with 0.127 g of PVP (Plasdone, supplied by International Specialty Products, 58,000 Mw), 6.5 g of BaSO4 and 81 mL of water. The solution is heated at 95° C. for 10 hrs and then placed into a mold. The mixture contained in the mold is then placed in a programmable environmental chamber and subjected to six successive freeze-thaw cycles ranging from +30° C. to −30° C. for 21 hours and 3 hours respectively. The gel so formed is then demolded and placed in a substantially isotonic osmotic aqueous solution of dextran for one day to osmotically balance the water content of the gel to a state similar to that of the human nucleus pulposus. Finally the prosthesis is packaged and sent for sterilization.
example 2
[0069] This example illustrates the basic mechanical properties of a hydrogel as prepared in Example 1.
[0070] Hydrogels often exhibit nonlinear mechanical properties and are highly deformable materials, and thus their properties are highly dependent on the testing and test conditions. A preferred hydrogel used in the invention was tested in the following manner to obtain the material incremental modulus. Tensile and compression properties were obtained as follows using a conventional mechanical testing machine.
[0071] A tensile test is performed on a sample 3.8 mm in diameter and 100 mm in length of a hydrogel prepared as in Example 1. The sample is gripped on both ends such that a 60 mm hydrogel gauge length exists between each grip. A preload of 0.04N is applied to the specimen. A tensile test is then performed on the specimen at a rate of 60 mm / min. The incremental tensile modulus is calculated as the slope of the line passing through points corresponding to the representative s...
example 3
[0073] This example illustrates the maintenance of the water content of the fully hydrated hydrogel of the invention under certain conditions of loading.
[0074] A 12 mm diameter material test specimen 8 mm in height is placed in a 37° C. bath of an isotonic aqueous solution. A stress relaxation study is performed on the specimen consisting of 15% displacement for 16 hours followed by 8 hours of unloaded recovery. The sample is tested through three successive cycles. Mass and modulus values are calculated before and after the three-cycle test. A plot of the conditions imposed in a typical testing cycle is presented in FIG. 14. The embodiment of the fully hydrated hydrogel as prepared in Example 1 shows less than 5% change in mass, modulus, and water content under this stress relaxation protocol.
Fatigue:
[0075] A fatigue study is performed to test for changes in water content under physiologic loading in the following manner. A 12 mm diameter test specimen 8 mm i...
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